This invention relates to fluorene copolymers, polymer blends comprising such copolymers, and electronic devices (such as polymer light emitting diodes) containing one or more films derived from these copolymers.
Conjugated polymers may exhibit the optical and electronic properties of inorganic semiconductors because of the presence of delocalized p-electrons. Poly(9,9-disubstituted-fluorene-2,7-diyls) constitute a family of semiconducting polymers with advantageous features. Their aromatic backbone is resistant to chemical and photochemical degradation; the biphenylene unit of each fluorene monomer is locked into a planar-like configuration by the C9 atom; substituents on C9 may be chosen to modify physical and chemical properties without introducing torsional strain between adjacent fluorene units which would otherwise be disruptive to delocalization of the p-system. Indeed, poly(9,9-di-n-octylfluorene-2,7-diyl) of U.S. Pat. No. 5,708,130 (herein fully incorporated by reference) has been shown to be an effective emitter for a blue light emitting diode (LED) (Grice, et.al Applied Physics Letters, Vol. 73, 1998, p 629-631) and to exhibit high carrier mobility, a very desirable feature for electronic devices (Redecker, et. al Applied Physics Letters, Vol. 73, 1998, pp. 1565-1567) each of which are fully incorporated herein by reference.
A means to further modify their optical and electronic properties is desired in order to broaden the applicability of these fluorene polymers in electronic devices. In this context, optical properties of a polymer include its absorption and photoluminescence spectra and electronic properties include ionization potential, electron affinity, band gap and carrier transport and mobility. U.S. patent application Ser. No. 08/861,469 filed May 21, 1997, U.S. Pat. No. 6,169,163 (herein fully incorporated by reference) teaches a way for property modification via fluorene copolymers each containing 9,9-disubstituted fluorene and another comonomer. For instance, copolymers comprising fluorene and aromatic amines have lower (closer to vacuum level) ionization potential and preferential hole transporting properties, and copolymers with cyano-containing moieties have higher electron affinity and preferential electron transporting properties relative to fluorene homopolymers.
Many electronic applications require the active material to exhibit both hole transporting and electron transporting properties. To maximize the efficiency of a LED, for example, the polymer should ideally transport both holes and electrons equally well (Bradley et. al, in Springer Series in Solid State Sciences, Vol 107, Springer-Verlag Berlin Heidelberg, 1992, pp. 304-309). The copolymers of U.S. patent application Ser. No. 08/861,469 filed May 21, 1997, herein fully incorporated by reference, comprising a fluorene moiety and one other comonomer cannot meet this requirement; therefore, there is a need for further improvement.
This invention relates to copolymers of 9-substituted and/or 9,9-disubstituted fluorene moieties and at least two other comonomers containing delocalized p-electrons. Preferably, at least 10% of the total monomeric units of these copolymers are selected from 9-substituted- and/or 9,9-disubstituted fluorenes; more preferably at least 15% of the monomeric units of these copolymers are selected from 9-substituted- and/or 9,9-disubstituted fluorenes; and most preferably at least 20% of the monomeric units of these copolymers are selected from 9-substituted- and/or 9,9-disubstituted fluorenes. Each copolymer contains two or more non-fluorene comonomers in any proportion. These copolymers are characterized by their excellent solubility ( greater than 1 g/L) in common organic solvents, ability to form pin-hole free films and weight-average molecular weight of at least 3000 gram/mole relative to polystyrene standard, preferably at least 10,000 gram/mole, most preferably at least 20,000 gram/mole. They are further characterized by a polydispersity of less than 10, preferably less than 5, most preferably less than 3. These copolymers exhibit photoluminescent emission in the range of 350 nm to 1,000 nm and absorption from 200 nm to 600 nm. The copolymers of this invention are useful as the active components in electronic devices including light emitting diodes, photocells, photoconductors, and field effect transistors.
This invention relates to fluorene copolymers and electronic devices comprising a film of such copolymers. The subject copolymers comprise at least 10%, based on residual monomeric units (RMU), of 9-substituted and/or 9,9-disubstituted fluorene moieties represented by structures I and II respectively. A residual monomeric unit is the portion of the monomer that is incorporated into the polymer backbone. For instance, 1,4-phenylene is the residual monomeric unit of 1,4-difunctional-benzene monomers irrespective of the chemical nature of the functional groups. 
In structures I and II, R1 and R2 are independently in each occurence hydrogen, C1-20 hydrocarbyl, C1-20 hydrocarbyloxy, C1-20 thiohydrocarbyloxy, or cyano. R1 and R2 are independently in each occurrence preferably hydrogen, C1-20 alkyl, C6-10 aryl or alkyl-substituted aryl, C6-10 aryloxy or alkyl-substituted aryloxy, C1-12 alkoxy/thioalkoxy, and cyano. Even more preferably R1 and R2 are independently in each occurrence hydrogen, C1-10 alkyl, phenyl, and cyano. R3 and R4 are independently in each occurrence a hydrogen, C1-20 hydrocarby optionally substituted with C1-20 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters; C6-20 aryl optionally substituted with C1-20 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters. R3 and R4may also form C3-12 cyclic structures with the olefin carbon (structure I) to which they are attached, said cyclic structures may further contain one or more heteroatoms such as phosphorus, sulfur, oxygen and nitrogen. Preferably R3 and R4 are independently in each occurrence a hydrogen, C1-12 alkyl optionally substituted with C1-12 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano and esters; C6-20 aryl optionally substituted with C1-12 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters. Most preferably R3 and R4 are independently in each occurrence a hydrogen, C1-8 alkyl optionally substituted with C1-10 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters; C6-12 aryl optionally substituted with C1-10 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters. R5 and R6 are independently in each occurrence a hydrogen, C1-20 hydrocarby optionally substituted with C1-20 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters; C6-20 aryl optionally substituted with C1-20 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters. R5 and R6 may also form C3-12 cyclic structures with the C-9 carbon of fluorene (structure II), said cyclic structures may further contain one or more heteroatoms such as phosphorus, sulfur, oxygen and nitrogen. Preferably R5 and R6 are independently in each occurrence a hydrogen, C1-12 alkyl optionally substituted with C1-12 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano and esters; C6-20 aryl optionally substituted with C1-12 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters. Most preferably R5 and R6 are independently in each occurrence a hydrogen, C1-8 alkyl optionally substituted with C1-10 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters; C6-12 aryl optionally substituted with C1-10 alkoxy/aryloxy, thioalkoxy/thioaryloxy, secondary/tertiary amines, hydroxy, carboxylic/sulfonic acids, cyano, and esters. These copolymers are characterized by their excellent solubility ( greater than 1 g/L) in common organic solvents, ability to form pin-hole free films and weight-average molecular weight of at least 3,000 gram/mole relative to polystyrene standard, preferably at least 10,000 gram/mole, most preferably at least 20,000 grain/mole. They are further characterized by a polydispersity of less than 10, preferably less than 5, most preferably less than 3. These copolymers exhibit photoluminescent emission in the range of 350 nm to 1,000 nm and absorption from 200 nm to 600 nm. The copolymers of this invention are useful as the active components in electronic devices including light emitting diodes, photocells, photoconductors, and field effect transistors.
In the first embodiment, the copolymers of the invention comprise at least 10% RMU of structures I and/or II and at least 1% of two or more RMUs possessing hole transporting property. Hole transporting property is imparted to a polymer by electron-rich RMUs. Examples include those derived from stilbenes or 1,4-dienes without electron-withdrawing substituents, tertiary amines, N,N,Nxe2x80x2,Nxe2x80x2-tetraaryl-1,4-diaminobenzene, N,N,Nxe2x80x2,Nxe2x80x2-tetraarylbenzidine, N-substituted-carbazoles, diarylsilanes, and thiophenes/furans/pyrroles without electron-withdrawing substitutents. These hole transporting RMUs may bear a variety of substituents so long as their presence do not significantly affect hole transporting properties adversely. Preferred substituents are C1-20 alkyls, C6-20 aryls and alkylaryls optionally substituted with C1-6 alkoxys and C6-12 aryloxys. Particularly effective are RMUs derived from tertiary aromatic amines, N,N,Nxe2x80x2,Nxe2x80x2-tetraaryl-1,4-diaminobenzene N,N,Nxe2x80x2,Nxe2x80x2-tetraarylbenzidine, thiophene, and bithiophene. Preferably the copolymers comprise at least 15% of RMUs of structures I and/or II, and at least 10% of two or more hole transporting RMUs. Most preferably the copolymers comprise at least 20% of RMUs of structures I and/or II and at least 20% of two or more RMUs possessing hole transporting property. The ratio of I to II may vary without limit and similarly the ratio of various hole transporting RMUs can vary without limit so long as the combined percentage in the copolymer remains within the specified range. With respect to the hole transporting RMUs in the copolymers of the invention, there is no restriction that they must all belong to the same chemical type. A copolymer of the invention may, for example, contain RMUs of the silanyl type, RMUs of the thiophene type and RMUs of the tertiary amine type.
In the second embodiment the copolymers of the invention comprise at least 10% of RMUs of structures I and II and at least 1% of two or more RMUs possessing electron transporting property. Electron transporting property is imparted to polymers by electron-deficient RMUs. Examples include RMUs containing electron-withdrawing groups such as F, cyano, sulfonyl, carbonyl, nitro, carboxy; moieties containing imine linkage, and condensed polycyclic aromatics. Condensed polycyclic aromatics include acenaphthene, phenanthrene, anthracene, fluoranthene, pyrene, perylene, rubrene, chrysene, and corene. Five-membered heterocylces containing imine linkages include oxazoles/isoxazoles, N-substituted-imidazoles/pyrazoles, thiazole/isothiazole, oxadiazoles, and N-substituted-triazoles. Six-membered heterocycles containing imine linkages include pyridines, pyridazines, pyrimidines, pyrazines, triazines, and tetrazenes. Benzo-fused heterocycles containing imine linkages include benzoxazoles, benzothiazole, benzimidazoles, quinoline, isoquinolines, cinnolines, quinazolines, quinoxalines, phthalazines, benzothiadiazoles, benzotriazines, phenazines, phenanthridines, and, acridines. More complex RMUs include 1,4-tetrafluorophenylene, 1,4xe2x80x2-octafluorobiphenylene, 1,4-cyanophenylene, 1,4-dicyanophenylene, and 
These electron transporting RMUs may bear a variety of substituents so long as their presence does not significantly affect electron transporting properties adversely. Preferred substituents are C1-20 alkyls, C6-20 aryls and alkylaryls optionally substituted with C1-6 alkoxys and C6-12 aryloxys. Particularly effective are RMUs derived from perfluorobiphenyl, quinoxalines, cyano-substituted olefins, oxadiazole, and benzothiadiazoles. Preferably the copolymers comprise at least 15% of RMUs of structures I and/or II, and at least 10% of two or more of the exemplified electron transporting RMUs. Most preferably the copolymers comprise at least 20% of RMUs of structures I and/or II and at least 20% of two or more of the exemplified electron transporting RMUs. The ratio of I to II can vary without limit and similarly the ratio of various electron transporting RMUs may vary without limit so long as the combined percentage in the copolymer remains within the specified range. With respect to the electron transporting RMUs in the copolymers of the invention, there is no restriction that they must all belong to the same chemical type. A copolymer of the invention may, for example, contain RMUs of the cyano-olefin type, RMUs of the oxadiazole type and RMUs of the condensed polynuclear aromatic type.
In the third embodiment, copolymers of the invention comprise at least 10% of RMUs of structures I and/or II and at least 1% of one or more hole transporting RMUs and at least 1% of one or more electron-transporting RMUs. Hole transporting RMUs and electron transporting RMUs are selected from among those already defined above. More preferably copolymers of this embodiment comprise at least 15% of RMUs of structures I and/or II and at least 5% of one or more hole transporting RMUs and at least 5% of one or more electron-transporting RMUs. Most preferably copolymers of this embodiment comprise at least 20% of RMUs of structures I and/or II and at least 10% of one or more hole transporting RMUs and at least 10% of one or more electron-transporting RMUs. The ratio of I to II can vary without limit and similarly the ratio of various hole transporting RMUs may vary without limit so long as the combined percentage in the copolymer remains within the specified range. With respect to the hole transporting RMUs in the copolymers of the invention, there is no restriction that they must all belong to the same chemical type. A copolymer of the invention may, for example, contain RMUs of the silanyl type, RMUs of the thiophene type and RMUs of the tertiary amine type. Similarly, with respect to the electron transporting RMUs in the copolymers of the invention, there is no restriction that they must all belong to the same chemical type. A copolymer of the invention may, for example, contain RMUs of the cyano-olefin type, RMUs of the oxadiazole type and RMUs of the condensed polynuclear aromatic type.
In the fourth embodiment, copolymers of the invention comprise at least 10% of RMUs of structures I and/or II, at least 1% of one or more RMUs derived independently in each occurrence from benzene, naphthalene, and biphenylene optionally substituted with C1-12 alkyl/alkoxy and C6-10 aryl/aryloxy (hereinafter referred to as arylene RMUs), and at least 1% of one or more RMUs selected from among the hole transporting and electron transporting RMUs defined above. Preferably copolymers of this embodiment comprise at least 15% of RMUs of structures I and/or II, at least 5% of one or more arylene RMUs, and at least 1% of one or more RMUs selected from among the hole transporting and electron transporting RMUs defined above. Most preferably copolymers of this embodiment comprise at least 20% of RMUs of structures I and/or II, at least 10% of one or more arylene RMUs, and at least 5% of one or more RMUs selected from among the hole transporting and electron transporting RMUs defined above. The ratio of I to II can vary without limit and similarly the ratio of various arylene RMUs may vary without limit so long as the combined percentage in the copolymer remains within the specified range. Incorporation of arylene RMUs can lead to modifications in the thermal, optical and electronic properties of the copolymers.
The fifth embodiment relates to blends of two or more of the copolymers of the invention without limits on relative proportions of the individual components. Such blends may be prepared by solution blending, or blending in the melt state.
The sixth embodiment relates to blends containing at least 0.1 weight % of at least one copolymer of the invention with at least one of the fluorene homopolymers or copolymers disclosed in U.S. Pat. Nos. 5,708,130, 5,777,070, and U.S. application Ser. No. 08/861,469. Such blends may be prepared by solution blending, or blending in the melt state.
The seventh embodiment relates to blends containing at least 0.1 weight % of at least one copolymer of the invention with at least one other non-fluorene polymer, e.g., polystyrene, polyethylene, poly(methyl methacrylate), polysulfones, polycarbonates, and polylurethanes. Such blends may be prepared by solution blending, or blending in the melt state.
The eighth embodiment relates to a film containing at least 0.1 weight % of at least one copolymer of the invention.
The ninth embodiment of the invention relates to light emitting diodes comprising one or more of the copolymers of the invention wherein the copolymers are present as single-layer films or as multiple-layer films, whose combined thickness is in the range of 10 nm to 1000 nm, preferably in the range of 25 nm to 500 nm, most preferably in the range of 50 nm to 300 nm. The copolymer films may be formed by solvent-based processing techniques such as spin-coating, roller-coating, dip-coating, spray-coating, and doctor-blading. When two or more copolymers are used, they may be deposited separately as distinct layers or deposited as one layer from a solution containing a blend of the desired copolymers. An organic light emitting diode typically consists of an organic film sandwiched between an anode and a cathode, such that when a positive bias is applied to the device, holes are injected into the organic film from the anode and electrons are injected into the organic film from the cathode. The combination of a hole and an electron may give rise to an exciton which may undergo radiative decay to the ground state by releasing a photon. The anode and the cathode may be made of any materials and in any structure known in the art. The anode is preferably transparent. A mixed oxide of tin and indium (ITO) is useful as the anode due to its conductivity and transparency. ITO is deposited on a transparent substrate such as glass or plastic so that the light emitted by the organic film may be observed. The organic film may be the composite of several individual layers or may be the blend of several materials each designed for a specific function. The cathode is commonly a metallic film deposited on the surface of the organic film by either evaporation or sputtering.
The tenth embodiment of the invention relates to photocells comprising one or more of the copolymers of the invention wherein the copolymers are present as single-layer fins or as multiple-layer films, whose combined thickness is in the range of 10 nm to 1000 nm, preferably in the range of 25 nm to 500 nm, most preferably in the range of 50 nm to 300 nm. The copolymer films may be formed by solvent-based processing techniques such as spin-coating, roller-coating, dip-coating, spray-coating and doctor-blading. When two or more copolymers are used, they may be deposited separately as distinct layers or deposited as one layer from a solution containing a blend of the desired copolymers. By photocells is meant a class of optoelectronic devices which can convert incident light energy into electrical energy. Examples of photocells are photovoltaic devices, solar cells, photodiodes, and photodetectors. A photocell generally comprises a transparent or semi-transparent first electrode deposited on a transparent substrate. A polymer film is then formed onto the first electrode which is, in turn, coated by a second electrode. Incident light transmitted through the substrate and the first electrode is converted by the polymer film into excitons which can dissociate into electrons and holes under the appropriate circumstances, thus generating an electric current.
The eleventh embodiment of the invention relates to metal-insulator-semiconductor field effect transistors comprising one or more of the copolymers of the invention (serving as the semiconducting polymer) deposited onto an insulator wherein the copolymers are present as single-layer films or as multiple-layer films whose combined thickness is in the range of 10 nm to 1000 nm, preferably in the range of 25 nm to 500 nm, most preferably in the range of 50 nm to 300 nm. The copolymer films may be formed by solvent-based processing techniques such as spin-coating, roller-coating, dip-coating, spray-coating and doctor-blading. When two or more copolymers are used, they may be deposited separately as distinct layers or deposited as one layer from a solution containing a blend of the desired copolymers. Two electrodes (source and drain) are attached to the semiconducting polymer and a third electrode (gate) onto the opposite surface of the insulator. If the semiconducting polymer is hole transporting (i.e., the majority carriers are positive holes), then applying a negative DC voltage to the gate electrode induces an accumulation of holes near the polymer-insulator interface, creating a conduction channel through which electric current can flow between the source and the drain. The transistor is in the xe2x80x9conxe2x80x9d state. Reversing the gate voltage causes a depletion of holes in the accumulation zone and cessation of current. The transistor is in the xe2x80x9coffxe2x80x9d state. If the semiconducting polymer is electron transporting (i.e., the majority carriers are electrons), then applying a positive DC voltage to the gate electrode induces a deficiency of holes (accumulation of electrons) near the polymer-insulator interface, creating a conduction channel through which electric current can flow between the source and the drain.
The copolymers of instant invention may be prepared by a variety of polycondensation processes. Particularly effective are those processes involving coupling of aromatic/vinylic/acetylenic monomers catalyzed by transition metals such as nickel and palladium.
Coupling of aryl and vinyl halides with zerovalent nickel was reported by Semmelhack et. al., (J. Am. Chem. Soc., Vol. 103, 1981, p. 6460-6471) herein fully incorporated by reference. Coupling of aryl halides and other heteroaromatic halides with zerovalent nickel was discussed by Yamamoto et. al., (Macromolecules, Vol. 25, 1992, p. 1214-1223) herein fully incorporated by reference. These procedures require a large excess of the air and moisture sensitive zerovalent nickel. A variant that requires a truly catalytic amount of nickel but a large excess of zinc as the reducing agent was first reported by Colon et. al., (J. Polym. Sci., Polym. Chem., Vol. 28, 1990, p. 367-383), herein fully incorporated by reference, and later applied successfully to fully conjugated polymers by Ueda et. al., (Macromolecules, Vol. 24, 1991, p. 2694-2697), herein fully incorporated by reference, represents an improvement with respect to experimental handling. In these procedures, mixtures of monomers each bearing two halogen substituents (preferably bromine and chlorine) can be polymerized into copolymers of essentially random nature if the monomers are of about the same reactivity. If reactivities are significantly different, then the more reactive monomers would be polymerized preferentially over the less reactive ones. The result would be a somewhat xe2x80x9cblockyxe2x80x9d copolymer of uncertain structure and order. An additional disadvantage of these procedures is the presence of large amounts of metallic reagents which must often be thoroughly removed from the resulting copolymers to avoid the deleterious effects they can have on electronic device performance.
Coupling reactions catalyzed by palladium are usually more preferred as the amount of palladium required is truly catalytic and the structure and order of the resulting copolymers are more predictable. Chen et. al., (Macromolecules, Vol. 26, 1993, p. 3462-3463), herein fully incorporated by reference, produced regiospecific polythiophenes by palladium catalyzed coupling of 2-bromo-5-(bromozinco)alkylthiophenes. The obtained molecular weights were very low, however. Coupling of aryl halides with acetylenes catalyzed by palladium was successfully used for producing copolymers by Yamamoto et. al., (Macromolecules, Vol. 27, 1994, p. 6620-6626), herein fully incorporated by reference, and coupling of aryl halides with olefins similarly employed for polymerization by Greiner et. al., (Macromol. Chem. Phys., Vol. 197, 1996, p. 113-134) herein fully incorporated by reference.
A preferred condensation reaction involves the coupling of organoboron compounds with organohalides as taught by Miyaura and Suzuki (Chemical Reviews, Vol. 95, 1995, p. 2457-2483) herein fully incorporated by reference. This reaction has been adapted with improvement to the production of high molecular weight polymers by Inbasekaran et. al., as reported in U.S. Pat. No. 5,777,070, herein incorporated in its entirety by reference. Polymerization is effected by reacting a near equimolar mixture of an aromatic/vinylic diboronic acid/ester (hereinafter referred to as type A monomer) and an aromatic/vinylic dibromide (hereinafter referred to as type B monomer). Two or more type A monomers and two or more type B monomers may be used so long as the combine molar amounts of A""s are approximately equal to that of B""s. A unique feature of copolymers from this process is the order which results from the fact that chain growth takes place exclusively via the formation of A-B dyads as each type A monomer can only react with a type B monomer. Monomers of more complex structures may be advantageously employed to yield copolymers of even higher degree of structural order. For example, an appropriately functionalized electron transporting RMU may be reacted with two molecules of a hole transporting moiety to yield a new monomer of the structure Br-HTRMU-ETRMU-HTRMU-Br, where HTRMU sand ETRMU stand for hole transporting RMU and electron transporting RMU respectively.